Glycidyl esters of α-branched monocarboxylic acids are useful for the preparation of epoxy, acrylic polyester and alkyd resins, either directly or via intermediate products such as adducts with (meth)acrylic acid amines, polyols and polyacids or as reactive diluents for the preparation of thermoset acrylic, epoxy polyester and/or urethane paints and coatings. Of particular interest are glycidyl esters of aliphatic monocarboxylic acids represented by the formula
wherein R1, R2 and R3 each represent the same or different alkyl radicals of normal or branched structure containing 1-20 carbon atoms, and R4 through R8 each represent hydrogen or a hydrocarbyl group containing 1-3 carbon atoms. A more preferred product is one where R1 through R3 are alkyl groups containing a sum total of 3-18 carbon atoms and where R4 through R8 are each hydrogen, e.g., the reaction product of neodecanoic acid (R1+R2+R3═C8) and epichlorohydrin.
The preparation of epoxy esters or also called glycidyl esters by reacting a mono- or polycarboxylic acid with an epoxyalkyl halide, such as epichlorohydrin, is well known. The process may be carried out in a single step with an alkali metal salt of the acid, as disclosed in U.S. Pat. No. 3,178,454. It should be realized, however, that many of the acids converted into glycidyl esters are soap-forming acids, with complicated preparation steps. The complications are due to foaming phenomena during water evolution. Moreover, there are problems in respect of caking and stirring complications due to the high viscosity of soap gel. This invention does not concern the process using a metal salt of the acid.
The epoxy esters may also be made by reaction of the carboxylic acid with an epoxyalkyl halide. This reaction involves the coupling of the epoxyalkyl halide to the acid group, whereby a halohydrin ester intermediate is formed. This is then followed by a second step involving a ring closure reaction (DHC). Typically, the reaction is then followed by one or more after treatments (ADHC) for the removal of any remaining halo functionality.
In U.S. Pat. No. 3,075,999 the process for the preparation of glycidyl esters of fatty acids is described. It comprises contacting an acid with an excess epoxyalkyl halide (an unsubstituted 1-halo-2,3-epoxyalkane of from 3 to 13 carbon atoms), in the presence of a catalyst at a temperature of 70 to 117° C. (boiling point of epichlorohydrin) while adding thereto an aqueous solution of an alkaline compound. The preferred catalyst is tetramethyl ammonium bromide and the preferred epoxyalkyl halide is epichlorohydrin (ECH). The equivalent ratio of ECH to acid may range from 15:1 to 2:1. In a typical experiment a tenfold excess of ECH is used, calculated on the acid. An equimolar amount of potassium hydroxide is added at reflux conditions and excess ECH and water are separated overhead. The products produced by this process have an Epoxy Group Content (EGC) of around 0.25 equivalent/100 g. This corresponds with a purity of around 87.5% (calculated on the actual EGC, divided by the theoretical EGC times 100%). They are produced at a reasonable high yield of 97% (calculated on the mol product divided by the mol acid times 100%). Although more then 40 years old, this process remains very attractive because of its simplicity. For instance, the water phase can be easily separated from the overhead and the excess ECH can be easily reused without the need for additional distillation steps and such. On the other hand, the EGC and hence the purity is low. It may be possible to improve the EGC by purifying the product, but this is at the detriment of the yield.
It is therefore the aim of the current invention, to find a process that is similar to this U.S. Pat. No. 3,075,999 process, but that yields glycidyl esters of branched monocarboxylic acids with a significantly higher EGC, in other words with a purity of at least 93.5%, preferably at least 94% and at a yield that is at least 95%, preferably at least 98% based on the starting fatty acid.
In CN 101245053 a method is disclosed for the preparation of neodecanoic acid glycidyl ester. The process involves dripping the neodecanoic acid (a mixture primarily composed of 2-ethyl-2,5-dimethylhexanoic acid) into a mixture of ECH, sodium hydroxide and catalyst, that is heated to 90° C. According to this reference, the reaction cycle is said to be short, the reaction yield is high, and the yield to be about 86 percent. However, upon study of this case, the current inventors found that the preparation method is not better than the old process of the US '999 reference. Thus, despite all recent developments, a need remains to improve the process for making glycidyl esters of branched monocarboxylic acids.
Interestingly, in WO 00/17179 a process is described for the preparation of glycidyl esters of alpha-branched monocarboxylic acids with a higher EGC. Again an epoxyalkyl halide is used in a molar excess (2-20, preferably 3-20, calculated on the acid). The reaction is carried out in the presence of a solvent and at a temperature in the range of from 30 to 110° C., preferably in the range from 65 to 95° C. A wide range of catalysts may be used, including alkali metal hydroxides, alkali metal carbonates, alkaline earth hydroxides, alkali metal or alkaline earth metal alcoholates; ammonium salts; and phosphonium halides, with alkali metal hydroxides and alkali metal alkanoates being preferred. A solvent, preferably an alkanol, is used to enable the dissolution of the catalyst of step (a). For instance, in Example 1 of this reference, a glycidyl ester is produced with an EGC of 4210 mmol/kg (i.e., purity of 96.2%), at a 96% yield, using a process involving isopropanol as solvent and fourfold excess of ECH. NaOH is added in a minor amount first, followed by cooling down and phase separation. After the subsequent alkali dosing the reaction product is separated again, into an aqueous phase and an organic phase. From this phase the excess ECH is removed by steam distillation and the product is treated with NaOH solution to convert the remaining hydrolysable chlorine. The organic phase is washed several times with water whereupon the organic phase is stripped with steam and dried. Without washing, as shown in Example 2 of this reference, the hydrolysable chlorine content increases. Without solvent, as shown in comparative example (a) of this reference, the hydrolysable chlorine content is even more than 5 times greater, whereas the EGC is only 2675 mmol/kg. From this reference it would therefore appear that a solvent is essential in order to reach a high EGC.
This reference, however, is silent as to the aspect of solvent removal and the energy requirements to distil said solvent. Interestingly, as shown in examples 6 to 11, the use of calcium hydroxide, tetramethyl ammonium chloride (TMAC) or ethyl triphenyl phosphonium iodide resulted in large amounts of residual acid and the salt thereof; the preparation of a glycidyl ester must therefore have been very limited, if any at all. This process has as a disadvantage that a solvent is required that must be removed during the process. The aim of the current inventors, on the other hand, is to improve the U.S. Pat. No. 3,075,999 process and to achieve an EGC similar to that in WO 00/17179, but without use of a solvent which adversely affects the economics of the process.
In CN 101085764 a method is disclosed for synthesizing (methyl)acroleic acid glycidic glyceride. It takes (methyl)glyceride as raw material, and reacts this with epichlorohydrin for ring opening and esterification under catalyst and inhibitor action. It then carries out ring-closure reaction with caustic soda to prepare (methyl)acroleic acid glycidic glyceride. Advantages of this method include low consumption of epichlorohydrin, no utilization of organic solvent during reaction, short process, simple operation, easy industrialization and little environmental pollution. The molar ratio of ECH to acid in the coupling reaction is 1-1.4:1. The temperature may vary from 60-100° C. An epoxy value of 0.503 eq/100 g is obtained, which corresponds with a purity of 71.4%. This is therefore a rather low EGC. Also the yield is rather poor: at about 26%. It would therefore seem that the process used in this reference is of little interest. Moreover, this reference does not concern the preparation of glycidyl esters of aliphatic branched monocarboxylic acids having at least 5 carbon atoms. The problem of purity and yield is not specifically addressed and specific measures to yield epoxy esters with an improved EGC at high yield are not as such mentioned.
EP 822189 A concerns a method for producing purified epoxy compound. Thus an epihalohydrin or 2-methylepihalohydrin is reacted with a compound having 2-4 carboxyl groups or 1-3 amido groups in the compound. Products are obtained at about 41% purity and 92% yield (example 1). This reference, once again, does not concern the preparation of glycidyl esters of aliphatic branched monocarboxylic acids having at least 5 carbon atoms. The problem of (relatively) low EGC is not encountered. Thus, specific measures to yield epoxy esters with an improved EGC at high yield are not as such mentioned.
JP 2003171371 concerns a method for producing alpha-monobranched saturated carboxylic glycidyl esters. The alpha-monobranched saturated aliphatic carboxylic glycidyl ester is produced by ring-opening reaction the acid and epihalohydrin in the presence of a catalyst and by ring-closing reaction of the halohydrin ester by using a dehydrohalogenation agent. Any excess epihalohydrin is removed before the product is treated with the dehydrohalogenation agent. The molar ratio of ECH to acid in the coupling reaction is 1.5-5.0:1, with all examples using an ECH at a molar ratio greater than 1.5. The temperature may vary from 30-120° C., whereas in the examples a temperature of about 80° C. is used. Although this application does address the issue of undesirable side-reactions, there remains a need for further improvement, in particular in respect of the yield and purity of the final glycidyl ester.
EP 475238 A concerns glycidyl esters of mono- and polycarboxylic acids containing one or more mesogenic moieties, curable compositions and cured compositions thereof. These glycidyl esters exhibit ordering of the molecular chains in the melt phase and/or in the advanced compositions thereof. This morphology is susceptible to orientation during processing which can result in enhanced unidirectional mechanical properties. In for instance example F, products are made at a purity of about 73% and a yield of about 74%. This reference does not concern the preparation of glycidyl esters of aliphatic branched monocarboxylic acids having at least 5 carbon atoms. Once again, specific measures to yield epoxy esters with improved purity at high yield are not as such mentioned.
According to DE 2127699 hydrolysis resistant glycidyl esters are prepared by catalytic reaction of mono- and/or polycarboxylic acids containing at least 1 carboxyl group bound to a tertiary or quaternary C-atom and epichlorohydrin, using 1-1.15 mol. epichlorohydrin to 1 carboxyl group equivalent, using water as reaction medium, followed by treatment with aq. alkali. The addition of the epichlorohydrin is carried out at a temperature of from 80-110° C., whereas in the examples a temperature of from 96 to 105° C. is used. The EGC is high, but at the detriment of the yield. In example 4 an “Epoxidzahl” of 18.7 is achieved. This corresponds to a purity of 98.7%. On the other hand, the yield is at most 95% or likely lower due to the distillation steps.
According to JP 57203077 a carboxylic acid and a little excessive amount of epichlorohydrin are heated to effect reaction to form a chlorohydrin ester, then the unreacted epichlorohydrin is recovered in the presence of an aqueous alkali and the dehydrochloric cyclization reaction is effect to give an alpha branched saturated fatty acid glycidyl ester. More specifically, a small amount of aqueous alkali is added to the reaction mixture and heated under reduced pressure to convert dichlorohydrin, a by-product, into epichlorohydrin which is distilled off azeotropically. Then, the remaining chlorohydrin ester is combined with an aqueous alkali and heated to effect dehydrochloric cyclization to give the titled substance. The molar ratios of epichlorohydrin to carboxylic acid in the two examples are 1.3:1 and 1.5:1. The preferred temperature for the coupling reaction is 70-140° C., whereas in the examples a temperature of 90 and 120° C. is used. A suggestion to improve the purity at high yield is not provided.
In JP 57130980 epoxyalkyl esters are prepared of branched carboxylic acids of formula R1R2R3C—COOH with a 3-6-fold molar amount of epichlorohydrin (ECH) by adding specific amounts of alkali metal hydroxide to the reaction system in three lots and recovering excess ECH before the third reaction step. This patent application is therefore rather typical of the prior art, wherein an excess of ECH is used.
GB 763559 is a very early reference on the preparation of glycidyl esters describing a process for preparing an epoxy ester of a carboxylic acid and a monohydric epoxy alcohol that comprises heating the carboxylic acid with at least two equivalent amounts of an epoxy mono-halogen compound, i.e., ECH, in the presence of a tertiary amine or a quaternary salt or a mixture thereof as a catalyst. As may be expected, a suggestion how to improve the purity at high yield is not provided.
U.S. Pat. No. 2,992,239 provides a method of preparing a glycidyl ester of long chain fatty acids which comprises: forming a mixture comprising a molten fatty acid containing at least ten carbon atoms, an alkali metal carbonate, and a quaternary ammonium halide catalyst in about the mol ratios of 1.0:1.0-1.5:0.0025-0.01, respectively; adding thereto from about 9 to about 13 moles of epichlorohydrin per mol of fatty acid; maintaining resultant mixture at a temperature above the melting point of the fatty acid until reaction substantially ceases, whereby said ester is formed, and recovering product glycidyl ester of said fatty acid from resultant solution. Like the references mentioned before, a suggestion how to improve the purity at high yield is not provided.
CN 1425729 relates to propylenyl pimaric acid diglycidic ester. This reference therefore does not concern the preparation of glycidyl esters of aliphatic branched monocarboxylic acids having at least 5 carbon atoms. The problem of (relatively) low purity and/or low yield is not encountered.
U.S. Pat. No. 6,570,028 describes a process for the manufacture of diglycidyl esters of alpha,alpha′-branched dicarboxylic acids, comprising (a) the reaction of the alpha,alpha′-branched dicarboxylic acid with a halo substituted monoepoxide such as an epihalohydrin, in a 1.1-20 acid equivalent ratio relative to the alpha,alpha′-branched aliphatic dicarboxylic acid. Purities of up to 93% have been achieved. Suggestions as how to improve the purity and yield in the preparation of glycidyl esters of aliphatic branched monocarboxylic acids have not been provided.
In U.S. Pat. No. 3,275,583 epoxy esters are used of the formula R1R2R3COO(CH2)xCR5/O\CR6R7 (wherein /O\ represents an oxirane ring). These epoxy alkyl esters may be prepared by reacting e.g., monocarboxylic acids and ECH in a stoichiometric ratio, to form a chlorohydrin, which may then be treated with alkaline substances to form the glycidyl ester. In this reference, on the other hand, glycidyl esters are prepared from crude carboxylic acids that have been neutralized with sodium hydroxide. Suggestions on the improvement of the purity and yield are not provided.
DE 1219481 discloses the preparation of glycidyl esters of soap-forming, particularly of dimerised and/or trimerised, fatty acids. They are prepared by the reaction of the appropriate fatty acids with excess epihalohydrin at elevated temperatures (reflux temperature) in the presence of a tertiary amine or a quaternary ammonium salt as catalyst. Products with a purity of up to 84% at a yield of 97% are disclosed (Example 1). Once again, suggestions on the improvement of the purity and yield of a glycidyl ester of a monocarboxylic acid are not provided.
More recently WO 2009/000839 discloses C9 alkanoic acid glycidyl esters and use thereof. According to this process, the acid is reacted with ECH in the presence of a chromium salt. The ECH ratio may be selected from 0.9 to 2 mol, preferably from 1 to 1.5 mol calculated on the acid. The reaction is carried out in solvent (acetonitrile) at 82° C. This reference therefore has the disadvantage that a solvent removal step needs to be included.
Despite the abundance of literature on the preparation of glycidyl esters of branched monocarboxylic acids, and despite the decades of preparation of said esters, the need remains for a simple and improved process that without having to use additional solvents, recycles or purifications steps produces said glycidyl esters in very high purity, i.e., at a purity greater than 93.5%, preferably greater than 94% (which corresponds with an ECG of about 4125 mmol/kg or greater) at a yield greater than 95%, preferably greater than 98%. This aim has been achieved by the process discussed hereinafter.